Add focused display option to shade display developer option

Adding a new option to the shade display developer setting that follows
the FocusedShadeDisplayPolicy (shade shows up on the last focused
display)

Bug: 391614971
Test: manual testing
Test: atest ShadeDisplaysRepositoryTest
Flag: EXEMPT bugfix
Change-Id: I0a0a602feecb80963d3397ada5ecd69f9cef02aa